Weight sensor assembly for determining seat occupant weight

ABSTRACT

A system for measuring the weight of a seat occupant is used to control airbag deployment. The system includes a plurality of weight sensors that have a first end mounted to a seat riser and a second end mounted to a seat frame or track member. The weight sensors have a central bendable portion that extends between the first and second ends. A groove is formed in one of the external surfaces of the central bendable portion to localize strain. A full bridge strain gage assembly is mounted on a surface of each of the weight sensors, opposite from the groove, for generating a weight signal in response to measuring deflection of the central bendable portion. A central processor determines seat occupant weight based on the weight signals and an airbag control module communicates with the processor. The control module controls deployment force of the airbag based on seat occupant weight.

RELATED APPLICATION

This application is a continuation of Ser. No. 09/598,087 filed on Jun.21, 2000, which claims priority to U.S. provisional application No.60/141,105 filed on Jun. 25, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an apparatus for measuring the weight of aseat occupant. Specifically, a sensor arrangement is mounted to a seatframe member to provide seat occupant weight measurements.

2. Related Art

Most vehicles include airbags and seatbelt restraint systems that worktogether to protect the driver and passengers from experiencing seriousinjuries due to a high speed collision. It is important to control thedeployment force of the airbags and the force of the seatbeltpre-tensioners based on the size of the driver or the passenger. One wayto control these forces is to monitor the weight of the seat occupant.If a smaller person such as a child or infant in a car seat is in thefront passenger seat, the weight on the seat will be less than if anadult occupies the seat.

Current systems for measuring the weight of a seat occupant are complexand expensive. One type of system uses pressure sensitive foil matsmounted within the seat bottom foam. Another system uses sensors placedat a plurality of locations within the seat bottom cushion. The combinedoutput from the mats or the sensors is used to determine the weight ofthe seat occupant. These sensors experience a substantially verticalforce, due to the weight of the seat occupant, but are also subject tolongitudinal and lateral forces caused by acceleration, deceleration, orturning. The lateral and longitudinal forces picked up by the sensorincorporate an error component into the weight measurement. The sensorsare very sophisticated using multiple strain gages and complicatedbending elements to provide high measurement sensitivity in the verticaldirection and low sensitivity to lateral and longitudinal forces inorder to increase accuracy.

Mounting these sensors within the seat bottom can also be difficult andtime consuming. It is difficult to find mounting locations for each thesensors that will accommodate all of the various positions of a seatedoccupant while still providing accurate measurements. Further, shiftingof the occupant on the seat can dislodge or move the sensors out oftheir proper location. Because the sensors are mounted within the seatbottom, it is difficult to reposition the sensors after the seat isinstalled in the vehicle.

Thus, it is desirable to have a simplified seat occupant weightmeasurement system that is accurate and easily to install and overcomesthe above references deficiencies with prior art systems.

SUMMARY OF THE INVENTION

In a disclosed embodiment of this invention, a system for measuring theweight of an occupant seated on a vehicle seat includes a seat elementmounted to a vehicle structure and a seat support member for supportinga seat bottom. A plurality of weight sensor assemblies are mountedbetween the seat element and the seat support member. Each of the weightsensor assemblies has a bottom surface and a top surface with a fullbridge strain gage mounted on one of the surfaces.

In a preferred embodiment, each weight sensor assembly has a first endmounted to the seat element, such as a seat riser, and a second endmounted to the seat support member, such as a seat frame or trackmember, with a central bendable portion extending between the first andsecond ends. The strain gages each generate a weight signal in responseto measuring deflection of the central bendable portion for therespective sensor assembly. A central processor determines the seatoccupant weight based on the weight signals. An airbag control modulecommunicates with the processor to control deployment force of an airbagbased on seat occupant weight.

In a further preferred embodiment, each of the sensors includes at leastone groove formed in one of the top or bottom surfaces. The grooveextends at least partially along the width of the sensor to localizestrain in the central bendable portion. The strain gage is placed on theother of the top or bottom surfaces, facing opposite from the groove.

The subject invention provides a simplified seat occupant weightmeasurement system that is inexpensive, accurate, and easily to install.These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an environmental view of a seat occupant seated in a vehiclehaving in airbag system.

FIG. 2 is an exploded view of a seat assembly incorporating the subjectweight measurement system.

FIG. 3 is a side view, partially cut-away, of the seat of FIG. 2 showingthe mounting of one sensor assembly.

FIG. 4 is a perspective view of the sensor assembly of FIG. 3.

FIG. 5 is a schematic diagram of the control system incorporating thesubject weight measurement system.

FIG. 6A is a top perspective view of a preferred embodiment of a sensorassembly.

FIG. 6B is a bottom perspective view of the sensor assembly of FIG. 6A.

FIG. 6C is a cross-section view of the sensor assembly taken along 6C—6Cof FIG. 6A.

FIG. 7 is an alternate embodiment of a weight sensor.

FIG. 8 is an alternate embodiment of a weight sensor.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

A vehicle includes a vehicle seat assembly, shown generally at 12 inFIG. 1, and an airbag system 14. The seat assembly 12 can be either adriver or passenger seat and includes a seat back 16 and a seat bottom18. When a vehicle occupant 20 is seated on the seat 12 a vertical forceFv is exerted against the seat bottom 18. The vertical force Fvrepresents the weight of the seat occupant 20.

The airbag system 14 deploys an airbag 24 under certain collisionconditions. The deployment force for the airbag 24, shown in dashedlines in FIG. 1, varies according to the weight of the occupant 20. Thevehicle includes a unique system for measuring the weight of the seatoccupant 20. This unique system is integrated into a seat frame or trackmember, generally indicated at 26 in FIG. 2.

The seat 12 is preferably mounted to a vehicle structure 30 on aninboard track assembly 26 a and an outboard track assembly 26 b that isspaced apart from the inboard track assembly 26 a by a predetermineddistance. Both the inboard 26 a and outboard 26 b track assembliesinclude first 28 and second 32 track members. The first track member 28is typically mounted to a seat riser 34 or directly to the vehiclestructure 30, such as a floor. The second track member 32 is mounted forsliding movement relative to the first track member 28 so that seat 12position can be adjusted forwardly and rearwardly within the vehicle toa desired position.

A plurality of sensor assemblies 36 are mounted between the first trackmembers 28 of the inboard 26 a and outboard 26 b track assemblies andthe riser 34. In the preferred embodiment, four (4) sensor assemblies 36are used with a first sensor assembly 36 a positioned near the front ofthe inboard track assembly 26 a, a second sensor assembly 36 bpositioned near the rear of the inboard track assembly 26 a, a thirdsensor assembly 36 c positioned near the front of the outboard trackassembly 26 b, and a fourth sensor assembly 36 d positioned near therear of the outboard track assembly 26 b.

Preferably, each sensor assembly 36 a, 36 b, 36 c, and 36 d has a firstend 40 mounted to the first track member 28 with at least one fastener42 and a second end 44 mounted to the riser 34 with at least onefastener 42, as shown in FIG. 3. It should be understood that any typeof fastener can be used and that other joining methods known in the artcan also be used to mount the sensors 36. A central bendable portion 46extends between the first 40 and second 44 ends of the sensor assembly36. As the vertical force Fv of the seat occupant 20 is exerted on theseat bottom 18, the central bendable portion 46 of each sensor assembly36 a, 36 b, 36 c, 36 d deflects or bends into an S-shaped configurationputting one portion of the sensor 36 in compression and another portionin tension.

In the embodiment of FIGS. 3 and 4, the first 40 and second 44 ends areraised above/below the central bendable portion 46 to form steps 38 oneach side of the central bendable portion 46. The height of the steps 38can be varied. This configuration forms gaps between the sensor 36 andthe track member 28 and between the sensor 36 and the riser 34 tofacilitate bending.

A strain gage 50 is mounted to each of the sensors 36 a, 36 b, 36 c, 36d to measure the amount of bending in the central portion 46. Thesensors 36 have a top surface 52 facing the seat bottom 18 and a bottomsurface 54 facing the riser 34. Preferably, a combination of four (4)strain gages, forming a full bridge, are mounted on one of the top 52 orbottom 54 surfaces to measure the bending. The four strain gages arethus combined to serve as a Wheatstone Bridge for measuring deflection.The operation of a Wheatstone Bridge is well known in the art.

As shown in FIG. 4, the stain gage 50 is mounted on the top surface 52of the sensor 36. A first aperture 56 is formed at the first end 40 ofthe sensor 36 and a second aperture 58 is formed at the second end 44 ofthe sensor 36 for receiving the fasteners 42. The strain gage 50 ispositioned between the apertures 56, 58 on the top surface 52. In orderto achieve more accurate readings, full-bridge strain gage 50 shouldhave all strain gage components mounted on only one surface of thesensor 36. In other words, if the strain gage 50 is mounted on the topsurface 52 then no strain gage components should be mounted on thebottom surface 54 or if the gage 50 is mounted on the bottom surface 54then no strain gage components should be mounted on the top surface 52.

The sensors 36 a, 36 b, 36 c, 36 d each generate a signal representativeof the occupant weight that causes bending at the respective location ofthe sensors 36 a, 36 b, 36 c, 36 d, see FIG. 5. Thus, the first sensor36 a generates a first signal 60, the second sensor 36 b generates asecond signal 62, the third sensor 36 c generates a third signal 64, andthe fourth sensor 36 d generates a fourth signal 66. The signals 60, 62,64, 66 are transmitted to a common interface unit 68 and are then fedinto a central processor unit or electronic control unit (ECU) 70 as isknown in the art. The ECU 70 combines the signals 60, 62, 64, 66 todetermine the weight of the occupant 20. The ECU 70 then sends a controlsignal 72 to a system controller 74. Preferably, the system controller74 is an airbag control module that is in communication with the ECU 70such that the deployment force of the airbag 24 is controlled based onseat occupant weight. The system controller 70 could also be used tocontrol the force of seat belt pretensioners based on occupant weight. Avehicle crash sensor 76 also supplies information to the airbag controlmodule 74 that is used in preparation for the control instructions forthe airbag 24. The system utilizes a power supply 78 as is known in theart.

A preferred embodiment of a weight sensor 136 is shown in FIGS. 6A-6C.In this preferred embodiment each of the sensor assemblies 136 a, 136 b,136 c, 136 d includes at least one groove 80 formed in one of the top 52or bottom 54 surfaces of the sensor 36. The groove 80 extends at leastpartially along the width of the sensor assembly 36 to localize strainin the central bendable portion 46. The full bridge strain gage 50 isplaced the opposing surface, facing an opposite direction from thegroove 80, see FIG. 6B. In this embodiment, the groove 80 extends acrossthe entire with of the sensor 36.

In an alternate embodiment of a weight sensor 236, shown in FIG. 7, apair of grooves 80 a, 80 b are formed in one of the top 52 or bottom 54surfaces to localize strain in the central bendable portion 46. Thegrooves 80 a, 80 b are spaced apart from one another and only extendpartially across the width of the sensor 36. In this embodiment, thestrain gage 50 is mounted between the grooves 80 a, 80 b.

In another alternate embodiment of a weight sensor 336, shown in FIG. 8,the sensor assembly 36 has a generally flat central bendable portion 46.A notch 84 is formed at one end that separates a pair of holes 86 thatare used to connect the sensor 36 to the interface 68.

The subject invention offers a simplified system for measuring theweight of a seat occupant 20. It is preferable to integrate the sensors36 between the track 28 and the riser 34 because they are commoncomponents for most vehicle seats 12. The subject weight measurementsystem is easily incorporated into any type of seat configuration. Themeasured weight is independent of seat position and is accuratelyprovided in various occupant positions on the seat 12.

By measuring the deflection in all four (4) locations in the inboard 26a and outboard 26 b track assemblies, it is possible to calculate theoccupant weight, which is proportional to the sum of the output of allof the sensors 36 a, 36 b, 36 c, 36 d. The electronics for signalconditioning and the interface 68 can be housed within the trackassemblies 26 a, 26 b as is well known in the art.

Although a preferred embodiment of this invention has been disclosed, itshould be understood that a worker of ordinary skill in the art wouldrecognize many modifications come within the scope of this invention.For that reason, the following claims should be studied to determine thetrue scope and content of this invention.

I claim:
 1. A system for measuring a weight on a vehicle seatcomprising: a seat having a seat bottom; a seat element for mountingsaid seat to a vehicle structure; a seat support member for supportingsaid seat bottom relative to said seat element; a sensor assemblymounted between said seat element and said seat support member andhaving a bendable central body portion for supporting at least onestrain gage for measuring strain resulting from a weight force appliedto said seat bottom, said bendable central body portion having apartially removed section to concentrate strain in said bendable centralbody portion wherein said partially removed section comprises a pair ofco-linear slots extending through said central body portion and spacedapart from each other across the width of said central body portion by amount surface.
 2. A system according to claim 1 wherein said strain gageis mounted on said mount surface between said slots.
 3. A systemaccording to claim 2 wherein said sensor assembly includes a first endfor attachment to said seat element and a second end for attachment tosaid seat support member, said bendable central body portion extendingbetween said first and second ends, and wherein said slots are formedwithin said central body portion approximately at an equal distance fromsaid first and second ends.
 4. A weight sensor assembly for measuring aweight on a vehicle seat comprising: a first end rigidly mounted to anupper seat structure; a second end rigidly mounted to a lower seatstructure; a deflectable central body portion extending between saidfirst and second ends and having an upper surface and a lower surface,said central body portion including a partially removed section forconcentrating strain at said central body portion resulting from aweight applied to said upper scat structure wherein said partiallyremoved section comprises a pair of co-linear slots extending throughsaid central body portion and spaced apart from each other across thewidth of said central body portion by a mount surface; and a strain gageassembly mounted on said central body portion for measuring the strainat said central body portion.
 5. An assembly according to claim 4wherein said strain gage assembly is mounted on said mount surfacebetween said slots.
 6. An assembly according to claim 5 wherein saidstrain gage assembly and said slots are both located at the middle ofsaid central body portion, approximately equal distances from said firstand second ends.
 7. A System for measuring a weight on a vehicle seatcomprising: a seat assembly having a seat bottom; a seat element formounting said seat assembly to a vehicle structure; a seat supportmember for supporting said seat bottom relative to said seat element; aplurality of weight sensor assemblies each including a first end rigidlymounted to said scat support member, a second end rigidly mounted tosaid seat element, a deflectable central body portion extending betweensaid first and second ends and having an upper surface and a lowersurface, said central body portion including a partially removed sectionfor concentrating strain at said central body portion resulting from aweight applied to said scat support member wherein said partiallyremoved section comprises a pair of co-linear slots extending throughsaid central body portion and spaced apart from each other across thewidth of said central body portion, and a strain gage assembly mountedon said central body portion between said slots for measuring the strainat said central body portion wherein each of said weight sensorassemblies generates a weight signal in response to measuring deflectionof said central body portion; a processing unit for receiving saidweight signals to quantify the weight applied to said seat assembly; andat least one safety device control module in communication with saidprocessing unit wherein deployment of at least one safety device iscontrolled by said safety device control module based on the weightapplied to said seat assembly.
 8. A system according to claim 7 whereinsaid slots and said strain gage assembly are both located at the middleof said central body portion, approximately equal distances from saidfirst and second ends.